1. Field of the Invention
The present invention generally relates to a sealing device in a wheel bearing for an automobile or the like and, more particularly, to the sealing device of a kind integrated together with an encoder grid.
2. Description of the Prior Art
The wheel bearing including, as shown in FIG. 37, a sealing device 105 interposed between an inner member 101 and an outer member 102 rotatable to each other through a circular row of rolling elements 103 has been well known in the art. The sealing device 105 shown therein includes an encoder grid 106 integrated together therewith. In this connections see the Japanese Laid-open Patent Publication No. 6-281018. The prior art sealing device 105 includes generally L-sectioned first and second annular sealing plates 107 and 108 fitted respectively to the inner and outer members 101 and 102 with an elastically deformable sealing lip member 109 secured to the second annular sealing plate 108 so as to intervene between the first and second annular sealing plates 107 and 108. The first annular sealing plate 107 is generally referred to as a slinger. The encoder grid 106 is made of an elastic material mixed with a powder of magnetic particles and is bonded by vulcanization to the first annular sealing plate 107. This encoder grid 106 is of an annular configuration having a plurality of pairs of magnetically opposite poles alternating over the circumference thereof and is cooperable with a magnetic sensor 110 disposed externally in face-to-face relation with the encoder grid 106 for detection of the encoder grid 106.
The first annular sealing plate 107 serving as the slinger and the inner member 101 serving as a rotatable member are engaged with each other under interference fit at an engagement interface 111. However, it has been found that a small quantity of water often ingresses externally into the wheel bearing through the engagement interface 111. Once water ingresses, the first and second annular sealing plates 107 and 108 gather rust, resulting a premature wear of the sealing lip member 109. Also, the grease is prematurely degraded to such an extent as to result in reduction of the lifetime of the wheel bearing.
In view of the foregoing, it has been suggested to reconfigure the encoder grid 106 so that a portion of the elastic material forming the encoder grid 106 extends to an inner peripheral surface of the first annular sealing plate 107 to thereby increase the sealability at the engagement interface 111. However, since the elastic material forming the encoder grid 106 is mixed with the powder of magnetic particles, not only becomes the encoder grid 106 expensive to manufacture, but a required sealing performance is difficult to attain. Also, formation of a relatively thick rubber layer at the engagement interface 111 between the first annular sealing plate 107 and the inner member 101 results in an insufficient engagement therebetween with the consequence that there is a high risk of the first annular sealing plate 107 being separated from the wheel bearing and/or displaced internally of the wheel bearing.
Although instead of the intervention of the elastic material the first annular sealing plate 107 may be made of a soft material to thereby increase the adherence, such soft material is normally of a non-magnetic nature and, therefore, the first annular sealing plate 107 made of such material will fail to provide a magnetic core for the encoder grid 106, resulting in an insufficient density of magnetic fluxes.
The first annular sealing plate 107 may exhibit a sufficient resistance to rusting if it is made of magnetic stainless steel (for example, SUS 430MA) of a kind having a resistance to rusting comparable to that of SUS 304, rather than a generally utilized magnetic material such as SUS 430 of a kind lacking a sufficient resistance to rusting. The magnetic stainless steel referred to above may be SUS 430MA consisting of a stainless steel such as SUS 430 mixed with niobium, Ni or the like to increase the resistance to rusting. As regards the magnetic flux density, SUS 430MA is comparable to SUS 430. However, not only is the magnetic stainless steel referred to above expensive, but even though such material is employed for the first annular sealing plate 107, ingress of water cannot be sufficiently prevented, and therefore, reduction of the lifetime of the wheel bearing as a result of degradation of the grease in contact with water cannot be avoided sufficiently.
FIG. 38 illustrates another prior art wheel bearing. In this figure, components identical with or similar to those shown in FIG. 37 are shown by like reference numerals used in FIG. 37. The sealing device 105 shown in FIG. 38 is shown as employed in the rolling bearing of a type having an inner race rotatable relative to an outer race. The sealing device 105 includes a slinger 107 press-fitted to an outer peripheral end face of the inner race 101, a core metal 108 press-fitted to an inner peripheral end face of the outer race 102 in face-to-face relation with the slinger 107, a sealing member 109 fitted to the core metal 108 and held in sliding contact with the slinger 107, and a rubber magnet 106 bonded by vulcanization to the slinger 107. The rubber magnet 106 referred to above is a pulse generating ring generally used for speed control of a vehicle such as, for example, an automobile. The slinger 107 is of a structure including an cylindrical body 107a having an outer edge formed integrally with a radial flange 107b that protrudes radially outwardly towards the outer race 102. The core metal 108 is of a structure including a cylindrical body 108a press-fitted to the inner peripheral end face of the outer race 102 and formed integrally with an radial flange 108b that protrudes radially inwardly towards the inner race 101 from an inner end thereof adjacent the circular row of the rolling elements 103. An outer end 108aa of the hollow cylindrical body 108a is slightly radially inwardly bent to accommodate the sealing member 109.
The sealing device 105 of the structure shown in FIG. 38 and described above is mounted in position inside the rolling bearing in the manner which will now be described. After the sealing device 105 has been assembled separate and independent of the rolling bearing, the sealing device 105 is press-fitted into the rolling bearing with the slinger 107 mounted on the inner race 101 and the core metal 108 fitted inside the outer race 102. During the press-fitting of the sealing device 105, a plurality of the sealing devices 105 stacked on a support table 114 as shown in FIG. 39 are delivered one by one into a chute by means of a handling unit of an automatic press-fitting machine and is then picked up to be press-fitted in the rolling bearing.
However, since the sealing device 105 shown in FIG. 38 is of a design integrated together with the rubber magnet 106, stacking on the support surface 114 (FIG. 39) the plural sealing devices 105 with the core metal 108 held in contact with the support surface 114 and with the slinger 107, bonded by vulcanization with the corresponding rubber magnet 106, positioned on one side of such core metal 108 remote from the support surface 114 results in contact of the rubber magnet 106 on the slinger 107 in one of the sealing devices 105 with the core metal 108 of the next adjacent sealing device 105 positioned immediately above such one of the sealing devices 105. Considering that the rubber magnet 106 exerts a magnetic force of attraction, the rubber magnet 106 in one of the sealing devices 105 attracts the core metal 108 in the next adjacent sealing device 105 positioned immediately above such one of the sealing devices 105 and, accordingly, a trouble often occurs in delivering the sealing devices 105 one by one by means of the handling unit of the automatic press-fitting machine, thereby hampering a smooth automatic press-fitting.
In view of the foregoing, the present invention has for its object to provide a sealing device for a wheel bearing effective to avoid any possible ingress of water through the engagement interface of the annular sealing plate to thereby increase the lifetime of the wheel bearing, substantially free from any possible problem associated with separation and/or displacement of the annular sealing plate and effective to secure a magnetic flux density.
The present invention has for its additional object to provide a sealing device for a rolling bearing effective to avoid any possible magnetic attraction between the neighboring sealing devices when the latter are stacked on a support table of the handling device so that the sealing devices can be transported into a chute one by one with no trouble to allow the individual sealing devices to be automatically press-fitted into the corresponding rolling bearings smoothly.
A wheel bearing according to a first aspect of the present invention includes an inner member, an outer member, a circular row of rolling elements interposed between the inner and outer members, and a sealing device for sealing an annular end space delimited between the inner and outer members. The sealing device includes:
first and second annular sealing plates secured respectively to one of the first and second members and the other thereof, and disposed in face-to-face relation to each other;
each of the first and second annular sealing plates including a cylindrical wall and a radial wall assembled together to represent a generally L-shaped section;
the first annular sealing plate being mounted on one of the inner and outer members which is rotatable relative to the other of the inner and outer members, with the radial wall positioned on one side adjacent an exterior of the bearing;
a first elastic member mixed with a powder of magnetic particles and bonded by vulcanization to the radial wall of the first annular sealing plate, the first elastic member being formed with a magnetized portion in which opposite magnetic poles are formed alternately in a direction circumferentially thereof;
the second sealing plate including an elastic sealing member, the elastic sealing member being formed integrally with a side sealing lip slidingly engageable with the radial wall of the first annular sealing plate and a radial sealing lip slidingly engageable with the cylindrical wall of the first annular sealing plate;
the cylindrical wall of the second annular sealing plate being spaced a slight radial gap from a free periphery of the radial wall of the first annular sealing plate; and
a second elastic material made of a material different from that of the first elastic member bonded to the radial wall and interposed at an engagement of the first annular sealing plate with such one of the first and second members which is rotatable.
According to the above described construction, since the radial wall of the first annular sealing plate is bonded by vulcanization with the first elastic member mixed with the powder of magnetic particles and magnetized to opposite magnetic poles alternating in a circumferential direction thereof, a so-called encoder grid is formed by the magnetized portion comprises of the first elastic member and rotation detection is possible with a magnetic sensor confronting the magnetized portion.
With respect to the sealing between the inner and outer members, a seal is obtained by sliding engagement of the various sealing lips provided in the second annular sealing plate with the first annular plate and by a labyrinth seal formed by disposition of the radial free periphery or free edge of the radial wall of the first annular sealing plate spaced a slight distance from the cylindrical wall of the second annular sealing plate to provide the radial gap.
As regards the engagement between the first annular sealing plate and the rotatable side member, the interposition of the second elastic member is effective to fill up minute interstices resulting from the shape and the surface roughness of the engagement, to thereby increase the effect of avoiding ingress of water. Since this second elastic member is made of a material different from that for the first elastic member mixed with the powder of magnetic particles to provide the encoder grid, a high sealability can be obtained by properly selecting the material. For this reason, without allowing the greases to be deteriorated in contact with water that has ingressed, the lifetime of the bearing can be increased. Also, since the second elastic member provides a sealing at the engagement, material for the first annular sealing plate is not limited and if the magnetic material is employed therefor, the magnetic flux density of the encoder grid formed by the elastic member provided in the radial wall thereof can be increased by such magnetic material.
In a preferred embodiment according to the first aspect of the present invention, the second elastic member interposed at the engagement of the first annular sealing plate may be a coated layer of rubber material applied to the first annular sealing plate.
If the second elastic member is comprised of the coated layer of rubber material, any possible reduction of the engaging force at the engagement of the first annular sealing plate, which would otherwise result from because of the second elastic member, can be avoided. For this reason, while the sealability be increased, any possible separation and/or displacement of the first annular sealing plate can also be avoided.
In another preferred embodiment according to the first aspect of the present invention, the second elastic member interposed at the engagement of the first annular sealing plate may be a layer of paint material applied to the first annular sealing plate and having a rust preventive property.
Even though the second elastic member is a layer of paint material, that is, a paint layer, any possible reduction of the force of engagement at the engagement of the first annular sealing plate, which would otherwise result from because of the second elastic member, can be avoided and, while the sealability be increased, any possible separation and/or displacement of the first annular sealing place can also be avoided. Also, since the paint material is of a kind having a rust preventive property, the first annular sealing plate can exhibit a rust proof and, therefore, the magnetic material can be selected for the first annular sealing plate with no possibility of being rusted
The paint material referred to above may be a polyethylene rubber paint.
In a further preferred embodiment according to the first aspect of the present invention, the second elastic member interposed at the engagement of the first annular sealing plate may be a layer of adhesive material applied to the first annular sealing plate and having a rust preventive property. The adhesive material referred to above may be a resinous room temperature setting adhesive having an anaerobic property.
Where the adhesive layer is interposed, the adhesive material effectively fill up minute interstices resulting from the shape and the surface roughness of the engagement, to thereby increase the force of engagement of the annular sealing plate to thereby increase the sealability. The resinous room temperature setting adhesive having an anaerobic property has a low cure rate when in contact with air, but can relatively quickly cure at room temperatures when applied to the engagement surface 18 where air is barely present. Accordingly, the size of a play between the first annular sealing plate and the inner or outer member engaged therewith for interference fit can be minimized to increase the assemblage.
In a still further preferred embodiment according to the first aspect of the present invention, the surface of the first annular sealing plate which forms the engagement preferably has a surface roughness not greater than Rmax. 3.0, where Rmax represents a maximum height of surface profile. The surface roughness may be chosen Rmax 0.5-2.2.
The more coarse the surface of the annular sealing plate, the higher the bonding strength of the second elastic member in the form of a thin film. However, if the surface of the annular sealing plate is too coarse, the dimensional precision of the surface of the annular sealing plate is lowered. Although hitherto the surface of the first annular sealing plate which forms the engagement has been chosen to be of Rmax greater than 3.0 and not greater than 7.5, selection of the surface roughness not greater than Rmax 3.0 is effective to maintain the dimensional precision of the inner diameter of the second elastic member while securing a sufficient bonding strength of the second elastic member.
In a still further preferred embodiment according to the first aspect of the present invention, the inner member may have an outer peripheral surface formed with an annular groove, and the second elastic member of the different material is a ring-shaped rubber member, and the first annular sealing plate is mounted on the inner member through the ring-shaped rubber member. When the annular groove is formed in the outer peripheral surface of the inner member, it is possible to cause the annular groove to trap water when the latter ingresses. Also, the sealability can be increased by the use of the ring-shaped rubber member mounted in the annular groove.
In a still further preferred embodiment according to the first aspect of the present invention, an annular joint between the cylindrical wall and the radial wall of the first sealing plate may be provided with a folded portion that extends radially inwardly from the radial wall and joined to the cylindrical wall after having been turned backwards and, on the other hand, an annular depression may be formed on an outer peripheral end surface of the inner member by radially inwardly depressing to provide a reduced diameter portion. In this case, the first annular sealing plate is mounted on the inner member with the folded portion positioned within the annular depression, and the second elastic member of the different material is a ring-shaped rubber member that is interposed between an annular side face of the annular depression and the folded portion.
When the first annular sealing plate is mounted on the inner member with the folded portion positioned within the annular depression in the manner described above, the passage for the flow of water represents a tortuous configuration, making it difficult for the water to ingress into the interior of the bearing. Also, the interposition of the ring-shaped rubber member between an annular side face of the annular depression and the folded portion is effective to provide a sufficient sealability. In addition, the provision of the folded portion is effective not only to increase the rigidity of the first annular sealing plate itself, but also the press work to form the first annular sealing plate can be performed with little elastic region (spring back) of the material left therein, and any possible deformation of the first annular sealing plate which would otherwise occur when heated to an elevated temperature during a subsequent heat treatment and/or vulcanization of the rubber material for the elastic member can advantageously be avoided. For this reason, the shape precision of the first annular sealing plate can be increased and the sealability due to engagement can further be increased.
In a still further preferred embodiment according to the first aspect of the present invention, an annular depression may be formed on an outer peripheral end surface of the inner member by radially inwardly depressing to provide a reduced diameter portion, and the first annular sealing plate may be mounted on the annular depression with the cylindrical wall thereof engaged with an outer peripheral surface of the annular depression. In this case, the second elastic member of the different material is preferably a ring-shaped rubber member that is interposed between an axial free end of the cylindrical wall of the first annular sealing plate and an annular side face of the annular depression.
In this structure, by allowing the second elastic member, in the form of the ring-shaped rubber member, to elastically contact the annular side face of the annular depression, even though dusts ingress through the engagement, further ingress thereof into the interior of the bearing can be prevented by the second elastic member. Also, since a major portion of the cylindrical wall of the first annular sealing plate is engaged directly on the inner member, a high force of engagement can be obtained. Thus, this structure is excellent in that any possible separation and/or displacement of the sealing plate can advantageously be prevented.
In a still further preferred embodiment according to the first aspect of the present invention, the cylindrical wall of the first annular sealing plate may be formed with a stop member which is in tun engaged in an annular groove defined on the outer peripheral surface of the inner member. By allowing the stop member to engage in the annular groove, any possible axial displacement of the first annular sealing plate can be avoided. For this reason, while the second elastic member is interposed at the engagement of the first annular sealing plate, any possible separation and/or displacement can be assuredly prevented.
The stop member referred to above may be comprised of a bent end formed at an axial free end of the cylindrical wall of the first annular sealing plate. If the stop member is represented by the bent end of the axial free end portion of the cylindrical wall of the first annular sealing plate, it can easily be formed. Also, since the stop member is provided at the axial free end of the cylindrical wall, the stop member will not provide any obstruction and the cylindrical wall can easily be mounted onto the inner member.
Alternatively, the stop member may be comprised of a plurality of protuberances formed on the cylindrical wall of the first annular sealing plate at a position generally intermediate of an axial length of the cylindrical wall and spaced a distance from each other in a direction circumferentially of the cylindrical wall of the first annular sealing plate. If the stop member is in the form of the plural protuberances, the stop member can easily be formed and formation of the stop member is effective to avoid any possible reduction of the area of surface of engagement.
Again alternatively, the stop member may be comprised of an annular projection formed in the cylindrical wall of the first annular sealing plate at a location generally intermediate of an axial length of the cylindrical wall and extending circumferentially of the cylindrical wall. Even when the stop member is in the form of the annular projection, the stop member can easily be formed. Also, when the stop member is in the form of the annular projection, the effect of preventing the first annular sealing plate from being displaced is high.
According to the second aspect of the present invention, there is provided a wheel bearing including an inner member, an outer member, a circular row of rolling elements interposed between the inner and outer members, and a sealing device for sealing an annular end space delimited between the inner and outer members. This sealing device includes:
first and second annular sealing plates secured respectively to one of the first and second members and the other thereof, and disposed in face-to-face relation to each other;
each of the first and second annular sealing plates including a cylindrical wall and a radial wall assembled together to represent a generally L-shaped section;
the first annular sealing plate being mounted on one of the inner and outer members which is rotatable relative to the other of the inner and outer members, with the radial wall positioned on one side adjacent an exterior of the bearing;
a first elastic member mixed with a powder of magnetic particles and bonded by vulcanization to the radial wall of the first annular sealing plate, the first elastic member being formed with a magnetized portion in which opposite magnetic poles are formed alternately in a direction circumferentially thereof;
the second sealing plate including an elastic sealing member, the elastic sealing member being formed integrally with a side sealing lip slidingly engageable with the radial wall of the first annular sealing plate and a radial sealing lip slidingly engageable with at least one of the cylindrical wall of the first annular sealing plate and the one of the inner and outer members which is rotatable;
the cylindrical wall of the second annular sealing plate being spaced a slight radial gap from a free periphery of the radial wall of the first annular sealing plate; and
the elastic sealing member having an elastic projection formed therewith so as to extend outwardly therefrom, the elastic projection being elastically engaged with a connecting member that is held in contact with an annular axial end face of the inner member.
In the case of this structure, similarly to the first aspect of the present invention, a so-called encoder grid is formed by the magnetized portion, and an effective sealing is attained by the sealing lips and a labyrinth seal between the first and second annular sealing plates. Also, by allowing the elastic projection protruding from the elastic member forming the magnetized portion to elastically engage the connecting member that is held in contact with the annular axial end face of the inner member, any possible ingress of water and/or dusts into the interior of the bearing can be prevented. Since the first annular sealing plate is engaged directly with the inner member with no elastic member intervening therebetween, there is no problem associated with reduction in the force of engagement.
The connecting member referred to above may be a constant speed universal coupling having a shoulder that is held in contact with the annular axial end face of the inner member.
Alternatively, the connecting member may be a crimped portion of a barrel hub which is crimpled radially outwardly to confront an axial end of a separate inner race then held in abutment with one end of the barrel hub. In this case, if the crimped portion is utilized as a member contactable with the elastic projection integral with the elastic member, the elastic projection need not be formed in a relatively large size and the elastic contact with the elastic projection is effective to provide a sealing capability.
In any one of the foregoing preferred embodiments according to the second aspect of the present invention, the elastic projection may be of a type elastically held in contact with an outer peripheral surface of the connecting member. Contact of the elastic projection with the outer peripheral surface of the connecting member does not require a dedicated portions on the connecting member to be prepared for contact with the elastic projection and the contact of the elastic projection can be accomplished, thereby enabling the sealing capability to be achieved with a simplified structure.
In any one of the foregoing preferred embodiments according to the second aspect of the present invention, the elastic projection may be elastically held in contact with a side face of the connecting member. Where the elastic projection is held in contact with the side face of the connecting member, the elastic member can be standardized without being restricted by the outer diameter dimension of the connecting member.
In any one of the foregoing preferred embodiments according to the second aspect of the present invention, the radial sealing lip of the second sealing plate may be slidingly engaged with the inner member. Sliding engagement of the radial sealing lip of the second sealing plate with the inner member is effective to further increase the sealability.
Also, in accordance with the third aspect of the present invention, there is provided a wheel bearing including an inner member, an outer member, a circular row of rolling elements interposed between the inner and outer members, and a sealing device for sealing an annular end space delimited between the inner and outer members. The sealing device employed in the wheel bearing according to the third aspect of the present invention includes:
first and second annular sealing plates secured respectively to one of the first and second members and the other thereof, and disposed in face-to-face relation to each other;
each of the first and second annular sealing plates including a cylindrical wall and a radial wall assembled together to represent a generally L-shaped section;
the first annular sealing plate being mounted on one of the inner and outer members which is rotatable relative to the other of the inner and outer members, with the radial wall positioned on one side adjacent an exterior of the bearing;
a first elastic member mixed with a powder of magnetic particles and bonded by vulcanization to the radial wall of the first annular sealing plate, the first elastic member being formed with a magnetized portion in which opposite magnetic poles are formed alternately in a direction circumferentially thereof;
the second sealing plate including an elastic sealing member, the elastic sealing member being formed integrally with a side sealing lip slidingly engageable with the radial wall of the first annular sealing plate and a radial sealing lip slidingly engageable with the cylindrical wall of the first annular sealing plate;
the cylindrical wall of the second annular sealing plate being spaced a slight radial gap from a free periphery of the radial wall of the first annular sealing plate; and
of the first and second annular sealing plates, at lest the first annular sealing plate being prepared from a steel plate made of a magnetic material, the steel plate having a surface formed with a metallic layer made of metal having a Yong""s modulus of elasticity that is lower than that for the one of the first and second members which is rotatable.
Again, according to the structure described above, a so-called encoder grid is formed by the magnetized portion, and an effective sealing is attained by the sealing lips and a labyrinth seal between the first and second annular sealing plates.
As regards the engagement between the first annular sealing plate and one of the inner and outer members which is on a rotatable side, although minute interstices resulting from the shape and the surface roughness are formed, surface indents forming the minute interstices can advantageously be filled by a soft metal forming the metallic layer since the metallic layer of a metal having a Young""s modulus of elasticity smaller than that of the rotatable side member is formed on the surface of the first annular sealing plate, thereby increasing the sealability. Accordingly, without allowing the greases to be deteriorated in contact with water that has ingressed, the lifetime of the bearing can be increased. Also, since a steel plate is employed as material for the first annular sealing plate, the magnetic flux density of the encoder grid can be increased. Since the metallic layer on the surface of the steel plate for the first annular sealing plate is thin, the magnetic flux density will not be little affected even though it is non-magnetic.
In a preferred embodiment according to the third aspect of the present invention, the metallic layer may be a metal plated layer. If the metallic layer is comprised of a metal plated layer, the metallic layer can easily be formed. Also, the metal having the low Young""s modulus of elasticity may be selected from the group consisting of zinc, tin, gold, silver and copper.
In another preferred embodiment according to the third aspect of the present invention, the metallic layer may have a thickness within the range of 5 to 30 xcexcm.
If the surface roughness of the engagement surface of the member on which the first annular sealing plate is mounted is about Rmax 3.0 (or Ra 0.63, where Ra represents a center line average height of surface profile), in order for the resultant minute surface irregularities to be filled up, the thickness of the metallic layer has to be at least not smaller than 5 xcexcm. On the other hand, even if this thickness is chosen to be not smaller than 30 xcexcm, effects brought about thereby remain the same and, conversely, the evenness or flatness will be adversely affected, requiring an increased length of time to form the metallic layer together with increase of the cost. For this reason, the thickness of the metallic layer is preferred to be within the above mentioned range. To form the metallic layer of a thickness within the range of 5 to 30 xcexcm, it is effective where the metallic layer is comprised of a metal plated layer.
In a further preferred embodiment of the present invention according to the third aspect of the present invention, a surface of the first annular sealing plate which forms the engagement may have a surface roughness not greater than Rmax 3.0, more preferably within the range of Rmax 0.5 to 2.2.
While such an annular sealing plate has hitherto been considered having a surface roughness of Rmax greater than 3.0 and not greater 7.5, increase of the degree of surface evenness or flatness is effective to allow the metallic layer to fill up the surface irregularities brought about thereby.
In a still further preferred embodiment of the present invention according to the third aspect of the present invention, a surface of the engagement of one of the first and second members, which is rotatable, with the first annular sealing plate may be formed as a ground surface which has been plunge cut.
With the plunge cutting, the raceway for the rolling elements in the rotatable member and the engagement surface are simultaneously formed by machining or grinding and, therefore, any misalignment therebetween can advantageously be avoided. In other words, if they are separately machined or ground, not only does a misalignment between the engagement surface, which eventually provides a sealing surface, and the raceway occur, but also there is a high risk of ingress of dusts when the engagement surface is machined or grinded without a sensor for sensing machined surface rendering the machined surface spiral. Since the plunge cutting is a technique in which a grinding wheel is applied at right angles to the work to be ground, the above discussed problems can advantageously eliminated.
Where the engagement surface of the rotatable member where the annular sealing plate is engaged therewith is defined by the plunge cut surface, it is desirable for the engagement surface to be finished to a surface roughness not greater than Rmax 3.0. This engagement surface as well is preferred to be within the range of Rmax 0.5 to 2.2. Even if the degree of the surface evenness of the engagement surface is increased, the function of the metallic layer to fill up the surface irregularities resulting from the surface roughness can be enhanced.
Again, in accordance with the fourth aspect of the present invention, there is provided a wheel bearing including an inner member, an outer member, a circular row of rolling elements interposed between the inner and outer members, and a sealing device for sealing an annular end space delimited between the inner and outer members. This sealing device used therein includes:
first and second annular sealing plates secured respectively to one of the first and second members and the other thereof, and disposed in face-to-face relation to each other;
each of the first and second annular sealing plates including a cylindrical wall and a radial wall assembled together to represent a generally L-shaped section;
the first annular sealing plate being mounted on one of the inner and outer members which is rotatable relative to the other of the inner and outer members, with the radial wall positioned on one side adjacent an exterior of the bearing;
a first elastic member mixed with a powder of magnetic particles and bonded by vulcanization to the radial wall of the first annular sealing plate, the first elastic member being formed with a magnetized portion in which opposite magnetic poles are formed alternately in a direction circumferentially thereof;
the cylindrical wall of the second annular sealing plate being spaced a slight radial gap from a free periphery of the radial wall of the first annular sealing plate; and
the second sealing plate including an elastic sealing member, the elastic sealing member being formed integrally with a side sealing lip slidingly engageable with the radial wall of the first annular sealing plate and a radial sealing lip slidingly engageable with an outer peripheral surface of the one of the inner and outer members, which is rotatable, and adjacent an engagement surface of the first annular sealing plate with such one member.
With this structure as described above, a so-called encoder grid is formed by the magnetized portion, and an effective seating is attained by the sealing lips and a labyrinth seal between the first and second annular sealing plates. Since of the elastic sealing lips, the radial sealing lip is held in sliding engagement with the outer peripheral surface adjacent the engagement of the rotatable side member with the annular sealing plate, even though water ingresses across the engagement between the first annular sealing plate and the rotatable side member, further ingress of the water into the interior of the bearing can be prevented by the sliding engagement of the radial sealing lip. For this reason, there is no possibility of the grease being degraded in contact with water and the lifetime of the bearing can be increased. Also, since the sealability can be secured by the radial sealing lip in this way, the material for the first annular sealing plate is not limited and any suitable magnetic material can be employed, allowing the magnetic flux density of the encoder grid, defined by the elastic member provided on the radial wall, to be increased.
In a preferred embodiment according to the fourth aspect of the present invention, an annular depression of a depth corresponding to a thickness of the first annular sealing plate is formed on the rotatable side, and the cylindrical wall of the first annular sealing plate is press-fitted around an outer peripheral surface of the annular depression. If the annular depression is provided and the first annular sealing plate is mounted thereon, any possible axial displacement of the first annular sealing plate towards the interior of the bearing can be prevented and, therefore, the axial position of the first annular sealing plate is limited, thereby securing a proper interference for the elastic side sealing lip. The annular depression referred to above has a small depth corresponding to the thickness of the cylindrical wall of the annular sealing plate, there is no problem associated with reduction in strength of the rotatable side member resulting from the formation of the annular depression and also with increase in size of the first annular sealing plate and also no problem associated with insufficient engagement which would otherwise result from an insufficient depth of the annular depression.
In another preferred embodiment according to the fourth aspect of the present invention, the radial sealing lip of the second sealing plate may be inclined so as to extend outwardly of the bearing. Where the radial sealing lip is inclined so as to extend outwardly of the bearing, as compared with the radial sealing lip inclined so as to extend in a reverse direction, that is, inwardly of the bearing, the effect of preventing water and dusts from ingressing exteriorly into the interior of the bearing can be increased.
In a further preferred embodiment according to the fourth aspect of the present invention, the side sealing lip of the second annular sealing plate may be provided at two locations spaced radially. The side sealing lip functions to prevent any possible flow of water from the outside of the bearing into the interior of the bearing and, therefore, the provision of this side sealing lip at two locations spaced radially inwardly and outwardly is effective to enhance the effect of preventing water ingress into the interior of the bearing.
In a still further preferred embodiment according to the fourth aspect of the present invention, the first annular sealing plate may be made of a ferrite stainless steel. Considering that the ferrite stainless steel is a ferromagnetic material, the use thereof as material for the first annular sealing plate is effective to increase the magnetic flux density of the elastic member defining the encoder grid.
In a still further preferred embodiment of the present invention according to the fourth aspect of the present invention, at least one of a free peripheral edges of the radial wall of the first annular sealing plate and the cylindrical wall of the second sealing plate may be provided with an overhang portion defined by a portion of the elastic member integrated with the annular sealing plate, in which case a maximum diameter portion of the free peripheral edge of the radial wall of the first annular sealing plate including this overhang portion has a diameter greater than a minimum diameter portion of an axial free end of the cylindrical wall of the second annular sealing plate and is positioned inwardly of the bearing from the minimum diameter portion.
According to this embodiment, since the radial sealing lip on the second annular sealing plate is held in sliding contact with the outer peripheral surface of the rotatable side member, and not held in sliding contact with the cylindrical wall of the first annular sealing plate, unless a countermeasure is taken, the first and second annular sealing plates will separate from each other while the sealing device has not yet been assembled into the bearing. For this reason, transportation and an assemblage of the sealing device into the bearing are complicated, accompanied by increase of manufacturing steps. In contrast thereto, since the overhang portion is engageable with the free end of the cylindrical wall of the second annular sealing plate in the axial direction, the possible separation between the first and second annular sealing plates can be prevented in a condition having not yet been assembled, and they can be dealt with as a single component part. Also, since the first and second annular sealing plates are engaged with each other in a manner that is unseparable from each other by means of the overhang portion integral with the elastic member, they can be assembled together or dismantled from each other by virtue of elastic deformation of the overhang portion. Also, the provision of the overhang portion renders the gap, forming the labyrinth seal, to represent a generally tortuous shape, resulting in increase of the sealability.
The present invention provides a sealing device that may be included in the wheel bearing according to any one of the first to fourth aspects of the present invention. In this sealing device, one of the first and second annular sealing plates which is on a fixed side may be made of a metal and such fixed side annular sealing plate or the elastic sealing member mounted thereon may be formed with a projection protruding inwardly of the wheel bearing, which projection is formed so as to be continuous or discontinuous.
It is to be noted that the projections referred to above may be formed integrally with the annular sealing plate.
According to the sealing device of the structure described above, when the sealing device is to be press-fitted to the bearing, a plurality of the sealing devices of an identical structure are placed on a support table, a space corresponding to the amount of protrusion of the annular projection protruding from the outer side face of the annular sealing plate fixed to the fixed member of the bearing and, therefore, the magnetic force of attraction acting to attract one of the sealing devices immediately above the magnetized portion of the other of the sealing devices stacked immediately above the magnetized portion thereof is weakened. Consequently, the neighboring sealing devices stacked on the support table will not be magnetically attracted with each other and, therefore, the sealing devices can advantageously be transported towards a chute by the handling unit of the automatic press-fitting machine one at a time and are then successively assembled into the respective bearings one at a time.
It is to be noted that in place of the first elastic member including the magnetized portion, the magnetized portion may be formed on the radial wall of the annular sealing plate, that is on the rotatable side, by directly magnetizing such radial wall of such annular sealing plate.
The present invention also provides a sealing device that may be included in the wheel bearing according to any one of the first to fourth aspects of the present invention. In this sealing device, one of the first and second annular sealing plates which is on a fixed side may be made of a metallic non-magnetic material.
According to the sealing device of the structure described above, the magnetic force of attraction emanating from the magnetized portion does not act on the annular sealing plate formed of the non-magnetic material and mounted on the fixed member of one of the sealing devices positioned above the other of the sealing devices. Consequently, the neighboring sealing devices stacked on the support table will not be magnetically attracted with each other.
The non-magnetic material is preferably in the form of an austenite stainless steel because it has a corrosion resistance effective to suppress rusting. Of the stainless steels available, SUS 304 is preferred because it is mass-produced and exhibits a required strength.